1. Technical Field
The present invention relates to a driving circuit of a stepping motor.
2. Background Art
In order to rotationally drive a stepping motor, a rotational torque must be applied. In particular, during an initial stage of rotation, a high rotational torque must be applied, but during a rotation retaining state where the stepping motor is continuously rotated, the rotational torque may be reduced. Therefore, there is an advantage that power consumption can be reduced by executing a control to reduce the applied current to the stepping motor during the rotation retaining state. In order to switch the applied current, it is necessary to switch a current-setting reference voltage of the driving circuit of the stepping motor.
FIG. 5 shows a structure of a driving circuit of a stepping motor of the related art. During the initial stage of rotation, a switch S1 is switched OFF to set a high voltage for the current-setting reference voltage VREF, and, during the rotation retaining state, the switch S1 is switched ON by a switch control signal X from the outside, to connect resistors R2 and R3 in parallel to each other and to consequently set a lower voltage value for the current-setting reference voltage VREF.
In the driving circuit of a stepping motor of the related art, a switch control signal X to the switch S1 must be generated by an external device (an electric device with the stepping motor equipped thereon) and applied to the switch S1. Because of this, the circuit structure of the external device (electronic device) becomes complicated, and there have been disadvantages for the manufacturers of the external device (electronic device), such as an increase in manufacturing cost.
In addition, there has been a disadvantage in that the ports (terminals) of the driving circuit of the stepping motor are occupied in order to input the switch control signal X to the switch S1.